A diesel engine may include one or more aftertreatment devices in an exhaust system coupled to the diesel engine. The aftertreatment devices may operate more efficiently when they are operating at temperatures that are greater than a threshold temperature (e.g., a light off temperature where aftertreatment device efficiency is greater than a threshold efficiency, such as 50%). One way to increase aftertreatment device temperature is to throttle the engine (e.g., partially close an engine intake throttle) and modify the start of fuel injection timing to adjust combustion phasing. However, engine noise, engine vibration, and engine efficiency metrics may limit the extent to which the engine out exhaust gas temperature may be increased to improve aftertreatment device efficiency.
Temperature of the aftertreatment device may also be increased via providing late post fuel injections (hereinafter referred to as LPIs) into the engine's cylinders. LPIs are injected after complete combustion of a main fuel injection pulse in a cylinder and before the exhaust valve(s) of a cylinder receiving the main fuel injection pulse closes during the cylinder's cycle. The LPIs may combust in the cylinder or in the exhaust system (e.g., within an oxidation catalyst) to elevate temperatures of exhaust gases that are directed to the aftertreatment device, thereby elevating the temperature of the aftertreatment device. However, injecting even small amounts of fuel in LPIs may increase the aftertreatment temperature more than is desired. Therefore, it is desirable to provide a way of increasing aftertreatment device temperature without increasing aftertreatment device temperature more than is desired.
The inventors herein have recognized the above-mentioned disadvantages and have developed an engine operating method, comprising: providing LPIs to all or fewer than all of the total number of engine cylinders available. This method is performed via a controller in response to feedback that providing a threshold amount of fuel in LPIs to each of the cylinders included in the total number of engine cylinders provides more fuel than is necessary to increase a temperature of an aftertreatment device a specified amount.
By providing LPIs to only a fraction of the total number of engine cylinders, it may be possible to increase a temperature of an aftertreatment device without increasing the temperature more than is desired. Further, fuel usage may be reduced since excess fuel may not be provided to increase the aftertreatment device temperature more than is desired. In one example, fuel supplied by fuel injectors may be supplied at minimum fuel pulse widths to ensure control of aftertreatment device temperature and repeatable delivery of small fuel amounts.
The present description may provide several advantages. In particular, the approach may allow for aftertreatment temperature control at low engine loads. In addition, the approach may decrease fuel consumption to heat aftertreatment devices. Further, the approach may reduce the possibility of producing more heat than may be desired in an aftertreatment device.
The above advantages, other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.